HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual page 124

• If you use 'x'% of the VLS to better fit into your backup window, what will that gain you in your
backup window and is that the best use of your VLS?
• You should do some backup tests to understand exactly how much the backups are sped up
through the introduction of the VLS into the environment before you can make this estimate
reasonably accurately.
• Compare the capacity required to hold the data that is most often restored to the VLS capacity.
If you use 'x'% of the VLS to speed up your restores, is that the best use of the VLS? How much
time in restores will this save? What does the ROI look like for this?
• Compare the capacity required to hold data that is backed up but has the shortest retention periods.
• If you use 'x'% of the VLS to reduce the amount of physical tape you create, is that the best
use of your VLS?
• To answer this, you should capture the cost of writing, tracking, storing (local and off-site), and
retrieving physical tapes.
Considerations
As you approach the sizing/capacity questions for VLS, see
in mind:
• When tuning performance, remember that the throughput of the VLS device is only one factor in
performance. The throughput may be very fast, but there are a myriad of other environmental
concerns that may gate throughput. The host/server, itself, may be slow, for example, or block
size may be an issue. Remember to take a holistic view of your environment.
• Hardware data compression is available with many VLS products, and it does not impede data
throughput. However, for VLS nodes that have been migrated to a VLS device with hardware
compression, the user must overwrite virtual tapes for the hardware compression to work.
Using data compression (2:1 ratio) will increase the backup capacity of the virtual tapes. For VLS
models without hardware compression, it can also reduce data throughput by up to 50% on a
VLS6000–series (in maximum configuration) compared to its native performance. For this reason,
the user must decide between maximum performance (compression disabled) or maximum capacity
(compression enabled).
• Excessive polling by other devices on the SAN (Windows 2003, for example) can have an ex-
tremely detrimental effect on performance.
• Above the entry-level VLS configuration, you need to have multiple concurrent backups going to
the VLS to achieve maximum throughput. Host speed multiplied by the number of concurrent host
backups equals the aggregate throughput requirement.
• Consider how many hosts you need to have running to keep the VLS optimized but not overloaded.
That is, don't try to back up more hosts than you have bandwidth for. If the throughput requirements
exceed the bandwidth, you may want to stage backups or increase the VLS capacity.
EVA Performance Sizing (VLS12000 Gateway)
To get the performance you need from the VLS12000 Gateway, you must also keep in mind the EVA
performance considerations:
• EVA tuning must be sized to the desired performance and must take into account the performance
of the arrays plus the compressibility of the data and whether deduplication is enabled or not
(deduplication requires double the array performance).
• An array at its maximum configuration will give full performance.
• The number of disks on the array can impact performance.
• To make the most of the system, there must be enough disk shelves in the EVA (12/14 disks per
shelf) to reach the required performance.
124 Virtual Library Systems
VLS Technical Specifications, and bear